The present invention generally relates to plastic articles having light reflecting surfaces. Particularly, the articles are made from a thermally-conductive polymer composition that can dissipate heat from a heat-generating light source within the articles. The reflector articles can be used as housings for automotive tail lamps and head lamps, flashlights, searchlights, and other lighting fixtures.
In the past, reflector articles or housings for lighting devices were made by stamping sheets of metal, for example, steel or aluminum, into a desired shape. Then, the surface of the metal could be buff-polished to form a reflective surface. This metal-stamping process produced reflector housings having good mechanical strength, but only a limited number of simple shapes could be made using this cumbersome process. Also, the polishing process could be time-consuming and expensive.
Today, reflector housings are often made from thermosetting or thermoplastic compositions that can be molded into a variety of complex shapes. Typically, these compositions contain a resin and a reinforcing material that improves the strength and dimensional stability of the molded reflector housing.
For example, Withoos et al., U.S. Pat. No. 4,188,358 discloses a method for making a metallized plastic reflector. A film or fabric of fibrous material (for example, glass or carbon fibers) is provided over a convex surface of a mold and saturated with a thermo-hardening synthetic resin. After partial hardening of the resin, a layer of liquid metal particles is sprayed onto the resin. A supporting layer including a synthetic resin reinforced with fibrous material (for example, polyester or nylon) is provided over the metal layer. After hardening of the assembly, the mold is removed.
Ohio et al., U.S. Pat. No. 4,364,637 discloses a method of making a highly reflective plastic reflector having a crystalline inorganic film coating. The method involves making a reflector having a molded body comprising a thermoplastic or thermosetting resin. The Patent discloses that the resins may be filled with reinforcing fillers such as glass fibers, mica, and asbestos. A light-reflective meal such as silver or aluminum is coated on one or all sides of the molded body. A light-transmissive film of an inorganic substance such as a metallic oxide or oxide of amphoteric elements is coated over the metallized coating.
Daniels et al., U.S. Pat. Nos. 4,507,254 and 4,570,203 disclose a method of making a light reflector for a photographic flash unit. The method involves molding a plastic housing using an injection-molding process. According to the patents, the reflector is shaped into its trough-like configuration by injecting liquid plastic into a mold. The plastic is allowed to solidify to form the plastic housing which maintains the contour of the reflector. The Patents disclose that polycarbonate can be used as the plastic in this manufacturing operation.
Ikeda et al., U.S. Pat. No. 5,945,775 discloses a lamp reflecting mirror suitable for use as a automotive head lamp, fog lamp, or the like. The Patent discloses that the lamp reflecting mirror is produced by injection-molding a composition containing 30 to 50% by weight of polyphenylene sulfide resin, 5 to 30% by weight of calcium silicate whiskers, and 20 to 65% by weight of granular inorganic filler.
As discussed above, conventional reflectors typically are coated with a light-reflective metal, such as aluminum, silver, chromium, and the like, using a vacuum-coating process. It is important for the reflector article to have a smooth surface so that the metallized, reflective coating can be uniformly deposited on the surface of the article. Many conventional reflector articles have rough and irregular surfaces, and it can be difficult to uniformly deposit the metallized coating onto such surfaces. There is a need for a reflector article having a smooth surface which will accept a metallized, light-reflecting coating easily. The reflective coating should be capable of being applied completely and uniformly to the surface of the reflector article. The present invention provides such a reflector article.
In addition, the light sources contained within reflector housings, for example, automotive tail lamps, can generate a tremendous amount of heat. Many reflector housings are made from molded plastics that are poor conductors of heat. As a result, heat remains trapped within this reflective area, and temperatures can quickly rise causing damage to the lighting device. There is a need for a thermally-conductive reflector that can effectively remove heat from heat-generating lamp assemblies. The present invention provides such a thermally-conductive reflector housing. The present invention also includes the thermally-conductive compositions and methods used to make such reflector housings. These and other objects, features, and advantages of the invention are evident from the following description and attached figures.